High voltage electrical insulators with flashover control means

ABSTRACT

The disclosed insulator comprises a series of cylindrical insulating members with barrier cushions interspersed therebetween. Each barrier cushion comprises an insulating disk of greater diameter than the insulating members. Conductive disks are disposed between the insulating members and the insulating disks. Each barrier cushion comprises a pair of such conductive disks, having outer edge portions welded together along an annular joint. The barrier cushions prevent propagation of a spark along the length of the insulator. The conductive disks have laterally projecting convolutions of generally cylindrical curvature, forming spark gaps. The spacing between the adjacent convolutions represents the least spacing between the electrically conductive disks of adjacent barrier cushions.

United States Patent Raymond G. Herb Madison;

James A. Ferry, Middleton, both of Wis. 873,216

Nov. 3, 1969 Sept. 28, 1971 National Electrostaties Middleton, Wis.

Inventors Appl. No. Filed Patented Assignee HIGH VOLTAGE ELECTRICALINSULATORS WITH FLASHOVER CONTROL MEANS 4 Claims, 3 Drawing Figs.

U.S. Cl 174/141, 310/6, 313/63, 328/233 Int. Cl ..H0lb 17/48, H02n 1/00,HOSh 7/00 Field of Search 174/140.

References Cited UNITED STATES PATENTS 8/1959 Nash 315/36 3,126,4393/1964 Denholm et a1. 174/142 X 3,473,064 10/1969 H61" 310/6 X FORElGNPATENTS 859,544 1/1961 Great Britain 313/249 Primary Examiner-- LaramieE. Askin Attorney-Burmeister, Palmatier & Hamby ABSTRACT: The disclosedinsulator comprises a series of cylindrical insulating members withbarrier cushions interspersed therebetween. Each barrier cushioncomprises an insulating disk of greater diameter than the insulatingmembers. Conductive disks are disposed between the insulating membersand the insulating disks. Each barrier cushion comprises a pair of suchconductive disks, having outer edge portions welded together along anannular joint. The barrier cushions prevent propagation of a spark alongthe length of the insulator. The conductive disks have laterallyprojecting convolutions of generally cylindrical curvature, formingspark gaps.

The spacing between the adjacent convolutions represents the leastspacing between the electrically conductive disks of adjacent barriercushions.

PATENTED SEP28 I97| FIG,

N VE/V T025 y Ja mond 6' Herb A. Harry M aiigs HIGH VOLTAGE ELECTRICALINSULATORS WITH FLASHOVER CONTROL MEANS This invention relates toelectrical insulators adapted to withstand extremely high voltages. Forexample, such insulators may be employed in high voltage electrostaticgenerators, adapted to produce several million volts.

It has been found that there is a tendency for high voltage insulatorsto break down due to the production of a minor electrical spark at somelocal point along the length of the insulator. The localized spark tendsto be propagated along the surface of the insulator so that a generalflashover, along the entire length of the insulator, is produced. Such aflashover can crack the entire insulator, or produce other severe damageso that it is necessary to shut down the generator to replace theinsulator. Flashover sparks are particularly damaging if they pass alongthe surface of the insulator and thus produce intense heating of theadjacent portion of the insulator.

It is one object of the present invention to provide a high voltageinsulator having barrier cushions which prevent the propagation of aspark along the surface of the insulator, so that the chance ofproducing a general flashover is greatly reduced.

A further object is to provide a high voltage insulator which issubdivided into a plurality of sections with cylindrically curved sparkgap electrodes therebetween, so that any sparking is virtually certainto occur between the spark gap electrodes, spaced a considerabledistance from the surface of the insulator, so that any sparks acrossthe spark gaps will not damage the insulator in any way.

Briefly outlined, the present invention preferably comprises a highvoltage insulator having a series of generally cylindrical insulatingmembers, with barrier cushions interspersed therebetween. Each barriercushion preferably comprises an insulating disk having a diametersubstantially greater than that of the insulating members, so that anyspark is forced outwardly and is prevented from being propagated alongthe entire length of the insulator. Electrically conductive disks ormembers are effectively wrapped around the outer portions of theinsulating disks so as to force the spark currents outwardly, away fromthe insulating members. Preferably, each barrier cushion comprises apair of electrically conductive disks, interposed between the insulatingdisk and the adjacent insulating members. The outer edge portions of thedisks are welded or otherwise secured together. Any spark currents willbe forced outwardly along the disks. The propagation of sparks isimpeded by the effective inductance of the disks.

Each electrically conductive disk is preferably formed with a spark gapelectrode in the form of a toroidal convolution, projecting laterallyfrom each disk toward the next barrier cushion in the series. Theconvolutions are cylindrical in curvature and are wrapped around theentire insulator so that continuous annular spark gap electrodes ofcylindrical curvature are provided on the barrier cushions. The sparkgap electrodes on adjacent barrier cushions are much closer togetherthan other portions of the barrier cushions, so that any sparks areforced to occur between the spark gap electrodes. The spark gaps arespaced a considerable distance outwardly from the surfaces of theinsulating members so that any sparks will not damage the insulatingmembers.

Further objects and advantages of the present invention will appear fromthe following description, taken with the accompanying drawings, inwhich:

F IG. 1 is a longitudinal section, taken through a high voltageinsulator to be described as an illustrative embodiment of the presentinvention.

FIG. 2 is a cross section, taken generally along the line 22 in FIG. I.

'FIG. 3 is a view similar to FIG. 1, but showing a modifiedconstruction.

As just indicated, the drawings illustrate a high voltage insulator 10,adapted to be employed in a high voltage electrostatic generator, or inany other situation in which the insulator must withstand extremely highvoltage gradients. The insulator 10 is sectionalized and thus comprisesa series of insulating members 12, with barrier cushions l4 interspersedtherebetween, The insulator 10 may be made as long as desired, simply byincreasing the number of sections in the insulator.

The insulating members 12 are preferably cylindrical in shape. They maybe either hollow or solid, as illustrated. The insulating members 12 maybe made of any suitable electrically insulating material, such asvarious ceramic materials. it is particularly advantageous to employ ahigh alumina ceramic material. Such a ceramic material generallycomprises in excess of percent aluminum oxide. However, it should beemphasized that other suitable insulating materials, particularlyceramic materials, may be employed.

Each barrier cushion 14 preferably comprises an insulating disk 16 and apair of electrically conductive members 18. As shown, the insulatingdisk 16 is sandwiched between the conductive members 18 which arepreferably made of metal. Each of the conductive members 18 is disposedbetween the insulating disk 16 and the adjacent insulating member 12.

The conductive members 18 are preferably formed with edge or peripheralportions 20 which are spot welded or otherwise secured together. Thus,the conductive members 18 are connected together both electrically andmechanically. However, the joint should preferably not be gastight, butrather should permit easy flow of the gaseous atmosphere around theinsulator. Such atmosphere often comprises a high pressure insulatinggas, such as sulfur hexafluoride, for example. It is desirable to enablethe high pressure gas to fill the space between the conductive members18.

The insulating disk 16 and the electrically conductive members l8prevent any localized spark from being propagated along the entirelength of the insulator 10. The insulating disk 16 and the conductivemembers 18 force the spark current outwardly, away from the outersurfaces of the insulating members 12. The effective inductance of theconductive members 18 impedes the propagation of any localized spark.Moreover, the insulating disk 16 is preferably larger in diameter thanthe insulating members 12, so as to prevent any spark from jumpingbetween the inner portions of the conductive members 18.

. The conductive members 18 are preferably formed so as to provide sparkgaps 22 between the adjacent barrier cushions 14. These spark gaps 22are formed by toroidal convolutions 24 projecting laterally away fromthe conductive members 18. Each spark gap 22 is formed between theconfronting convolutions 24 on adjacent barrier cushions 14. The spacingbetween the convolutions or electrodes 24 is considerably smaller thanthe spacing between other portions of the barrier cushions 14, so thatany sparks are forced to jump across the gaps 22, between theconvolutions 24.

The convolutions 24 are preferably cylindrical in curvature, but arewrapped around the insulator 10 so as to be annular in form. As viewedin cross section, the illustrated convolutions 24 are generallysemicircular in form- The spark gap 22 between each pair of confrontingconvolutions 24 extends around the entire circumference of the insulator10 so that any spark, however localized, will be forced to jump acrossthe gap 22.

The electrically conductive members 18 are suitably bonded or otherwisesecured to the insulating members 12 and disks 16. It is preferred toform each conductive member or disk 18 with a central aperture 26 sothat the bonds between each member 18 and the insulating elements 12 and16 are not forced with the central portions of the insulating elements.The apertures 26 are of assistance in preventing any rocking movementbetween the conductive members [8 and the insulating members 12 and 16,before and during the formation of the bonds.

Any suitable method may be employed to form the bonds between the metaland insulating members. Those skilled in the art will be familiar withvarious methods, such as soldering and the use of adhesives, forexample. The bonding material is shown at 28 in FIGS. 1 and 3.

It will be appreciated that all of the elements of insulator 10 may bestacked and bonded together simultaneously in a single bondingoperation. The resulting insulator will withstand exceptionally highvoltages, because the barrier cushions l4 prevent the propagation of anylocalized spark. The insulating disks l6 and the metal members 18 of thebarrier cushions 14 force any such spark outwardly, away from thesurfaces of the insulating members 12. if any spark occurs, it will jumpacross one of the spark gaps 22, which are spaced outwardly from theinsulating members 10, so that there will be no damage to any of theinsulating members.

In order to utilize the high voltage insulators to best advantage, it ispreferred to employ a potential distribution system, s that the voltagegradient along each insulator will be substantially constant. Fig. 1shows a potential distribution system which may be employed when theinsulators are used in a high voltage electrostatic generator. Normally,such a high voltage generator employs a plurality of the insulators,arranged to provide parallel supporting posts. Potential distributionrings 30 are preferably employed to interconnect the correspondingbarrier cushions 14 of the various insulators. The rings 30 extendaround the insulators and are suitably connected to the conductivemembers 18 of the barrier cushions 14. As shown in FIG. 1 for example,the rings 30 are welded to the outer flange portions of the barriercushions 14.

In order to provide a substantially uniform potential gradient along theinsulators, means are provided to cause a small current to flow alongthe insulators, between each pair of barrier cushions 14. In FIG. 1,corona gaps 32 are utilized to provide such currents. Each corona gap 32is formed by a needle-point electrode 34 and a flat disk electrode 36.As shown, each disk 36 is circular in shape and is formed with roundededges. The disks 36 are spot welded, riveted or otherwise secured to thecorresponding barrier cushions 14. Specifically, as shown in FIG. 1,each disk 36 is spot welded to the outer flange portion 20 of one of theconductive members 18. The needle-point electrodes 34 may simply bepress fitted into central openings 38 in the disks 36. Any othersuitable arrangement may be employed to mount the needle-pointelectrodes on the disks 36.

Preferably, each needle point 34 provides the negative electrode of eachcorona gap 32, while the next disk 36, opposite the needle point 34,forms the positive electrode.

The needle-point electrodes 34 cause corona discharges to occur acrossthe gaps 32. The resulting corona currents are small, but are sufficientto equalize the potential drops between the adjacent barrier cushions14. For example, the voltage drop between the successive barriercushions may amount to about 50 kilovolts.

FIG. 3 illustrates a modified arrangement in which resistors 40 areemployed instead of the corona gaps 32 of FIG. 1. The resistors 40 areconnected between the conductive members 18 of the successive barriercushions 14. Those skilled in the art will be familiar with suitableresistors, adapted to withstand the high voltages which are developedbetween the adjacent barrier cushions. The resistors permit the flow ofsmall cur rents which are sufficient to equalize the voltage dropsbetween the successive barrier cushions. The resistors 40 are usuallymuch longer then the interval between the successive barrier cushions l4and are mounted diagonally between the barrier cushions of differentinsulators. This arrangement is made possible by the potentialdistributing rings 30 which insure that the corresponding barriercushions of all the insulators are at the same potential.

We claim: 1. An insulator for high voltages, said insulator comprising aseries of generally cylindrical insulating members, and a series ofbarrier cushions interspersed between said insulating members to preventthe propagation of a spark along the outer surfaces of said insulatingmembers, each barrier cushion comprising an insulating CilSk having adiameter substantially greater than that of the adjacent insulatingmembers,

and electrically conductive members extending around the outer sides ofsaid insulating disks,

said electrically conductive members of each barrier cushion comprisinga pair of electrically conductive disks disposed between said insulatingmembers and said insulating disks,

said electrically conductive disks having outer annular portions weldedtogether along an annular joint extending around the correspondinginsulating disk.

2. An insulator according to claim 1 in which said electricallyconductive disks are formed with laterally projecting toroidalconvolutions of generally cylindrical curvature in cross section,

said convolutions of each pair of adjacent barrier cushions forming anannular spark gap therebetween.

3. An insulator for high voltages,

said insulator comprising a series of generally cylindrical insulatingmembers,

and a series of barrier cushions interspersed between said insulatingmembers to prevent the propagation of a spark along the outer surface ofsaid insulating members,

each barrier cushion comprising an insulating disk having a diametersubstantially greater than that of the adjacent insulating members,

and electrically conductive members extending around the outer sides ofsaid insulating disks,

said electrically conductive disks having outer annular portionsengaging each other and rigidly secured together along an annular jointextending around the corresponding insulating disk.

4. An insulator according to claim 3,

in which said electrically conductive disks are formed with laterallyprojecting toroidal convolutions of generally cylindrical curvature incross section,

said convolutions of each pair of adjacent barrier cushions forming anannular spark gap therebetween.

1. An insulator for high voltages, said insulator comprising a series ofgenerally cylindrical insulating members, and a series of barriercushions interspersed between said insulating members to prevent thepropagation of a spark along the outer surface of said insulatingmembers, each barrier cushion comprising an insulating disk having adiameter substantially greater than that of the adjacent insulatingmembers, and electrically conductive members extending around the outersides of said insulating disks, said electrically conductive members ofeach barrier cushion comprising a pair of electrically conductive disksdisposed between said insulating members and said insulating disks, saidelectrically conductive disks having outer annular portions weldedtogether along an annular joint extending around the correspondinginsulating disk.
 2. An insulator according to claim 1, in which saidelectrically conductive disks are formed with laterally projectingtoroidal convolutions of generally cylindrical curvature in crosssection, said convolutions of each pair of adjacent barrier cushionsforming an annular spark gap therebetween.
 3. An insulator for highvoltages, said insulator comprising a series of generally cylindricalinsulating members, and a series of barrier cushions interspersedbetween said insulating members to prevent the propagation of a sparkalong the outer surface of said insulating members, each barrier cushioncomprising an insulating disk having a diameter substantially greaterthan that of the adjacent insulating members, and electricallyconductive members extending around the outer sides of said insulatingdisks, said electrically conductive disks having outer annular portionsengaging each other and rigidly secured together along an annular jointextending around the corresponding insulating disk.
 4. An insulatoraccording to claim 3, in which said electrically conductive disks areformed with laterally projecting toroidal convolutions of generallycylindrical curvature in cross section, said convolutions of each pairof adjacent barrier cushions forming an annular spark gap therebetween.